1. Field of the Invention
The present invention relates to a mobile communications system and, more particularly, to a method and apparatus for providing at least one mobile communication terminal, or user equipment (UE), with a point-to-multipoint multimedia service through two or more common physical channels in a mobile communications system.
2. Description of the Related Art
FIG. 1 is a block diagram of a network structure of a universal mobile telecommunications system (UMTS). Referring to FIG. 1, the universal mobile telecommunications system (hereinafter, referred to as ‘UMTS’) includes a user equipment 1 (hereinafter, referred to as ‘UE’), a UMTS terrestrial radio access network 2 (hereinafter, referred to as ‘UTRAN’) and a core network 3 (hereinafter, referred to as ‘CN’). The UTRAN 2 includes at least one radio network sub-system 4 (hereinafter, referred to as ‘RNS’) and each RNS includes a radio network controller 5 (hereinafter, referred to as ‘RNC’) and at least one base station 6 (hereinafter, referred to as ‘Node B’) managed by the RNC. The Node B 6 includes at least one cell.
FIG. 2 is an architectural diagram of a radio interface protocol between a UE 1 and UTRAN 2 based on the 3GPP (3rd Generation Partnership Project) radio access network specifications. Referring to FIG. 2, the radio interface protocol horizontally includes a physical layer, a data link layer and a network layer and the radio interface protocol vertically includes a user plane for data information transfer and a control plane for signaling transfer. The protocol layers in FIG. 2 can be divided into L1 (first layer), L2 (second layer), and L3 (third layer) based on lower three layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The physical layer as the first layer provides an information transfer service to an upper layer using physical channels. The physical layer is connected to a medium access control (MAC) layer above the physical layer via transport channels through which data are transferred between the medium access control layer and the physical layer. Data is transmitted between different physical layers, and more particularly, between the physical layer of a transmitting side and the physical layer of a receiving side via physical channels.
The medium access control (MAC) layer of the second layer provides services to a radio link control (hereinafter abbreviated RLC) layer above the MAC layer via logical channels. The RLC layer of the second layer supports reliable data transfer and is operative in segmentation and concatenation of RLC service data units (SDUs) sent down from an upper layer.
A radio resource control (RRC) layer located on the lowest part of the third layer is defined in the control plane only and controls the logical channels, the transport channels, and the physical channels with configuration, reconfiguration, and release of radio bearers (RBs). An RB is a service offered by the second layer for the data transfer between the UE 1 and the UTRAN 2. Generally, configuring an RB refers to defining the characteristics of protocol layers and channels necessary for providing a specific service and is to establish respective specific parameters and operational methods for them.
A multimedia broadcast/multicast service (hereinafter, referred to as ‘MBMS’) offers a streaming or background service to a plurality of UEs 1 using a downlink dedicated MBMS bearer service. An MBMS is provided during one session, and data for the MBMS is transmitted to the plurality of UEs 1 via the MBMS bearer service during an ongoing session only. A UE 1 performs activation first for receiving the MBMS to which the UE has subscribed and receives the activated services only.
The UTRAN 2 provides the MBMS bearer service to at least one UE 1 using radio bearers. The radio bearers (RBs) used by the UTRAN 2 include a point-to-point radio bearer and a point-to-multipoint radio bearer.
The point-to-point radio bearer is a bi-directional radio bearer and is configured by a logical channel DTCH (dedicated traffic channel), a transport channel DCH (dedicated channel), and a physical channel DPCH (dedicated physical channel) or a physical channel SCCPCH (secondary common control physical channel). The point-to-multipoint radio bearer is a unidirectional downlink radio bearer and is configured by a logical channel MTCH (MBMS traffic channel), a transport channel FACH (forward access channel), and a physical channel SCPCH. The logical channel MTCH is configured for each MBMS offered to one cell and is used for transmitting user-plane data of a specific MBMS to a plurality of UEs.
As illustrated in FIG. 3, a logical channel MCCH (MBMS control channel) in a conventional system is a point-to-multipoint downlink channel used in transmitting control information associated with the MBMS. The logical channel MCCH is mapped to the transport channel FACH (forward access channel), while the transport channel FACH is mapped to the physical channel SCCPCH (secondary common control physical channel). A cell has only one MCCH.
The UTRAN 2 providing MBMS services transmits MCCH information through the MCCH channel to at least one UE 1. The MCCH information includes notification messages, specifically RRC messages related to the MBMS. For example, the MCCH information may include messages indicating MBMS service information, messages indicating point-to-multipoint radio bearer information or access information indicating that RRC connection for the MBMS is needed.
FIG. 4 is a diagram illustrating how MCCH information is transmitted in a conventional method. FIG. 5 illustrates a conventional method for providing an MBMS.
As illustrated in FIG. 4, the UTRAN 2 providing an MBMS service transmits the MCCH information to a plurality of UEs 1 via the MCCH channel. The MCCH information is periodically transmitted according to a modification period and a repetition period.
The MCCH information is categorized into critical information and non-critical information. The non-critical information can be freely modified each modification period or each repetition period. However, the critical information can be modified only each modification period.
Specifically, the critical information is repeated one time each repetition period. However, the modified critical information can be transmitted only at a start point of the modification period.
The UTRAN 2 periodically transmits a physical channel MICH (MBMS notification indicator channel) to indicate whether the MCCH information is updated during the modification period. Therefore, a UE 1 attempting to receive only a specific MBMS does not receive the MCCH or MTCH until a session of the service begins but receives the MICH (MBMS notification indicator channel) periodically. The update of the MCCH information refers to a generation, addition, modification or removal of a specific item of the MCCH information.
Once a session of a specific MBMS begins, the UTRAN 2 transmits an NI (notification indicator) through a MICH. The NI is an indication to a UE 1 attempting to receive the specific MBMS that it is to receive an MCCH channel. The UE 1, having received the NI via the MICH, receives an MCCH during a specific modification period indicated by the MICH.
The MCCH information is control information, specifically RRC messages, associated with an MBMS. The MCCH information includes MBMS modification service information, MBMS non-modification service information, MBMS point-to-multipoint RB information and access information.
A UE 1 attempting to receive a specific MBMS using a point-to-multipoint radio bearer receives MCCH information including radio bearer information via an MCCH and then configures the point-to-multipoint radio bearer using the received information. After configuring the point-to-multipoint radio bearer, the UE 1 keeps receiving a physical channel SCCPCH, to which an MTCH is mapped, in order to acquire data of the specific MBMS transmitted via the MTCH.
As illustrated in FIG. 6, a UTRAN 2 in a conventional system may transmit MBMS data discontinuously via the MTCH. In doing so, the UTRAN 2 periodically transmits a scheduling message to UEs 1 via an MSCH, specifically a SCCPCH carrying MTCH, to which an MTCH is mapped. The scheduling message indicates a transmission start timing point and transmission period of MBMS data transmitted during one scheduling period. The UTRAN 2 should previously inform the UE of a transmission period, specifically a scheduling period, of scheduling information.
The UE 1 obtains the scheduling period from the UTRAN 2 and then receives scheduling messages according to the scheduling period periodically. The UE 1 receives a SCCPCH carrying a MTCH discontinuously and periodically using the received scheduling messages. Specifically, according to the scheduling messages, the UE 1 receives the SCCPCH carrying the MTCH during times for which data is transmitted but does not receive the SCCPCH carrying the MTCH during times for which data is not transmitted. Using the above-described scheme, the UE 1 can receive data efficiently so that battery consumption may be diminished.
In the conventional method described above, a WCDMA system using a FDD (Time Division Duplex) mode transmits the SCCPCH using a channel code. This results in restricting the maximum transmission speed of an MBMS transmitted through the SCCPCH below 256 kbps, which is the maximum speed of the SCCPCH. Therefore, a disadvantage of the conventional method is that an MBMS service exceeding 256 kbps cannot be provided.
Therefore, there is a need for an apparatus and method that facilitates providing an MBMS service exceeding 256 kbps. The present invention addresses this and other needs.